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air operated points

kevinbennett

Joined: 9-10-16

Topics: 6

Replies: 8

Posted: Mon 11th Dec 2017, 8:04pm
air operated points

We will, hopefully, be rebuilding the track at Evergreens Miniature railway, the idea of making the points air operated (instead of the old windscreen wiper motors)
Whats peoples thoughts? ... is this a good, bad or indifferent idea?
 

Replies To This Post

Mick

Joined: 1-01-89

Topics: 8

Replies: 144

Posted: Mon 11th Dec 2017, 9:44pm

we have had air operated points at Abbeydale for many years, controlled from the signal box or in some case remote switching to operate the solenoid air valves. Obviously a compressor is needed and suitable air pipe work installed. Happy to provide more information if needed.
 

kevinbennett

Joined: 9-10-16

Topics: 6

Replies: 8

Posted: Mon 11th Dec 2017, 10:04pm

Thanks Mick for your input .... any problems to watch out for? ... someone has mentioned the problem of condensation freezing in the system, has this every been an issue?
 

Mick

Joined: 1-01-89

Topics: 8

Replies: 144

Posted: Tue 12th Dec 2017, 8:28am

We have never had problems with freezing although our latest compressor has an automatic draining facility. The air needs in-line lubrication to assist the cylinders and valves to work efficiently. If you are trailing a point there must be springing between the piston and the tie bar to avoid damage to the cylinder, otherwise the blade is just held against the stock rail by air pressure. We operate at 80 lbs/sq in
 

MartynRedfearn

Joined: 1-01-94

Topics: 20

Replies: 133

Posted: Tue 12th Dec 2017, 2:14pm

We have air operated signals and point for many years no great issues other than replacing the odd compressor and slow operation of the on furthest from the signal box. We have now moved onto linear actuators, cheap source for some brand new ones being the main reason for change and that they were simpler to make than our old design.
 

colinedmondson

Joined: 9-08-09

Topics: 3

Replies: 86

Posted: Wed 13th Dec 2017, 9:58pm

Think about taking an air line direct to points that are some distance away and operating themn by a solenoid valve adjacent to the point, it removes the slow operation caused by a long pipe from the signal box acting as a reservoir.
 

RussCoppin

Joined: 19-09-01

Topics: 0

Replies: 10

Posted: Sun 17th Dec 2017, 12:19am

The setup at Millerbeck is as follows:
Two main compressors run between 95 and 120 psi and feed the main airline in a ring around the site via a regulator set at 90psi along with a filter and oiler using 8mm airline.
There are three main substations each with a small (8L) compressor, a manifold for the air solenoids and then a one way valve from the main incoming airline. All airline to the points/signals is 4mm and ideally regulated to about 30psi which is enough to hold the point blades over but will not cause a derailment if trailed with the cylinder we are using.
The small compressors run between 70-80psi so only kick in if there is a problem with the main air line which is set to 90psi. This greatly speeds up the priming of the system thanks to the one way valve and they only run for about 30 seconds to fill the local sections while the main airline may take 10 minutes to fill.
There are additional filters and oilers before the air goes into the solenoids and the longest run from the solenoid to cylinder is about 30m.
All the signals, control panel and compressors (via contactors) come on via a single switch in the signal box which turns on the 24V supply around the site. This comes from two large batteries which will keep the system powered for hours should the mains go off and there is enough air in the system to run for about half an hour and get all passengers safely back to the station.

In the past there was no battery backup so if the mains went off or just blipped the route would reset and potentially change a point under a train. We have also had air lines freeze due to build up of condensation and the only solution to this is fitting filters and regularly cleaning them and blowing down the system.

If you hear one of the small compressors running after the initial power up you know there is a local fault and where to start looking which is very handy. We did make provision for indicator lights on the signal panel to show when each compressor was running but haven't got round to that yet and the little ones are noisy enough to hear!

If someone were to put a spade through the main air line then the small compressors will happily run everything by themselves. All the airlines and cabling are in conduit and at least a foot deep to try and protect from frost. All the compressors will easily keep up with a couple of 4mm pipes venting. All points and signals operate within a second even on the longest run whereas on the old system the furthest point/signal took 15 seconds.

I hope this info helps and if you need anything more then give me a shout.
 

kevinbennett

Joined: 9-10-16

Topics: 6

Replies: 8

Posted: Tue 19th Dec 2017, 7:17pm

Many thanks for all your inputs .... something to think about over Xmass :-)
 

johnnicholson

Joined: 1-01-77

Topics: 13

Replies: 76

Posted: Tue 19th Dec 2017, 10:42pm

What Russ did not say is that Millerbeck use 4 mm air pipe for local distribution and 8 mm air pipe for the ring main.
 

RussCoppin

Joined: 19-09-01

Topics: 0

Replies: 10

Posted: Fri 22nd Dec 2017, 5:04am

Sizes were mentioned John but I was squeezing a lot of info into the post and trying not make it too long.
That is a fairly key part though as the 8mm ring main acts as a large reservoir feeding the solenoids and the 4mm going out.

It is also worth mentioning the quality of the pneumatic parts is important. The new system has now been in for 2 years and already several of the cheaper ebay fittings from China have had to be replaced as they have either cracked or started leaking. Being able to isolate different air lines is very useful but the quarter turn isolation valves we got have been rubbish and there's probably 20 of them in the system. All the Festo and other branded parts have been faultless so far so the quite large difference in price is actually worth it. The same can also be said for relays and other components.
 
 
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